The present invention concerns methods for improving cardiac function and reducing the occurrence of pulseless electrical activity after the delivery of a defibrillation pulse to a subject.
Sudden cardiac death (SCD) accounts for an estimated 200,000 to 400,000 deaths annually in the United States alone. The initial cardiac rhythm in the majority of SCD cases is ventricular fibrillation (VF). Only approximately 10% of all SCD victims will be discharged from the hospital despite prompt CPR, a good emergency medical system response time, and use of automatic external defibrillators.
Approximately 50% of SCD patients will be treated with a defibrillator, by which they are administered a defibrillation waveform. Of the xe2x80x9csuccessfulxe2x80x9d defibrillations, approximately 50% will exhibit an electrical pulse as demonstrated by an electrocardiogram, but will not exhibit a physical pulse as demonstrated by restored, peripherally measured, blood pressure. This condition is known as xe2x80x9cpulseless electrical activityxe2x80x9d (PEA) or xe2x80x9celectromechanical dissociationxe2x80x9d (EMD). Only approximately 8% of individuals with post-shock PEA survive to be discharged from the hospital. Hence, there is a clear need for ways to reduce the frequency or likelihood of onset of PEA to thereby increase the efficacy of defibrillation.
PCT Application WO 00/66222 to Rosborough and Deno describes a method and apparatus for treatment of cardiac electromechanical dissociation in which a first treatment signal to terminate a techyarrhythmia is administered to the heart of a subject, blood flow is measured, and if the measured blood flow is below a predetermined amount then a second signal, such as a series of packets of electrical pulses, is administered. One problem with such an approach is the need to wait until after defibrillation to monitor the patient before deciding whether to administer the post-treatment packets of pulses to treat the electromechanical dissociation.
U.S. Pat. No. 5,314,448 to Kroll et al. describes a process for defibrillation pretreatment of a heart in which an electrical pretreatment of a fibrillating heart is applied. The pretreatment is said to begin organizing the action of the chaotically contracting myocardial cells so that the defibrillating waveform applied after the pretreatment can accomplish its task with less energy than would otherwise be required. This reference is concerned with reducing shock energy and capacitor size for implantable defibrillation systems. This reference is not concerned with external defibrillation systems, is not concerned with treating PEA, and is not concerned with increasing the efficacy of defibrillation.
U.S. Pat. No. 5,978,705 to KenKnight et al. descries a method for treating cardiac arrhythmia in which an auxiliary pulse is delivered in conjunction with a primary pulse, with the auxiliary pulse being delivered to a weak field area relative to the primary pulse. The object of the auxiliary pulse is to alter the intrinsic patterns of recovery of excitability and thereby momentarily yield localized cessation of propagation by inactivating sodium ion conductance channels via elevation of the transmembrane potential (see, e.g., column 8, lines 59-66). This reference is not concerned with the treatment of PEA.
Accordingly, there remains a need for new ways to treat and reduce pulseless electrical activity, particularly PEA following the administration of a defibrillation waveform.
A first aspect of the present invention is a method of reducing the likelihood of onset of pulseless electrical activity after defibrillation in a subject afflicted with a fibrillating heart. The method comprises administering to a subject afflicted with fibrillation a first treatment waveform, the first treatment waveform insufficient to defibrillate the heart; and then administering to the subject a second treatment waveform that defibrillates the heart and restores organized electrical activity in the heart. The first treatment waveform reduces the likelihood of onset of pulseless electrical activity following the second treatment waveform, as compared to that likelihood which would be present in the absence of the first treatment waveform.
A second aspect of the present invention is a system for the defibrillation of the heart of a patient in need of such treatment. The system comprises a power supply and a controller operatively associated with the power supply, the controller configured for delivering a defibrillation sequence comprising a first treatment waveform, the first treatment waveform insufficient to defibrillate the heart, and then a second treatment waveform that defibrillates the heart and restores organized electrical activity in the heart. The first treatment waveform reducing the likelihood of onset of pulseless electrical activity following the second treatment waveform as compared to that likelihood which would be present in the absence of the first treatment waveform.
A third aspect of the present invention is a method for the external defibrillation of the heart of a patient afflicted with ventricular fibrillation. The method comprises externally administering to the patient a first treatment waveform, the first treatment waveform insufficient to defibrillate the heart, and then externally administering to the subject a second treatment waveform that defibrillates the heart and restores organized electrical activity in the heart.
A fourth aspect of the present invention is an external defibrillation system for the external defibrillation of the heart of a patient afflicted with ventricular fibrillation. The system comprises a power supply and a controller operatively associated with the power supply. The controller is configured for delivering a defibrillation sequence comprising a first treatment waveform, the first treatment waveform insufficient to defibrillate the heart, and then a second treatment waveform that defibrillates the heart and restores organized electrical activity in the heart.
A fifth aspect of the present invention is a method of reducing the likelihood of onset of pulseless electrical activity after defibrillation with an implantable defibrillator in a subject afflicted with a fibrillating heart. The method comprises the steps of administering to a subject afflicted with fibrillation a first treatment waveform, the first treatment waveform insufficient to defibrillate the heart, and then administering to the subject a second treatment waveform that defibrillates the heart and restores organized electrical activity in the heart. The first treatment waveform reduces the likelihood of onset of pulseless electrical activity following the second treatment waveform as compared to that likelihood which would be present in the absence of the first treatment waveform.
A sixth aspect of the present invention is an implantable defibrillator for defibrillating the heart of a subject in need thereof. The defibrillator comprises a power supply and a controller operatively associated with the power supply. The controller is configured for delivering a defibrillation sequence comprising a first treatment waveform, the first treatment waveform insufficient to defibrillate the heart; and then a second treatment waveform that defibrillates the heart and restores organized electrical activity in the heart. The first treatment waveform reduces the likelihood of onset of pulseless electrical activity following the second treatment waveform as compared to that likelihood which would be present in the absence of the first treatment waveform.
A further aspect of the present invention is a defibrillation system for the defibrillation of the heart of a patient afflicted with ventricular fibrillation. The system comprises a detector for detecting electrical activity from the heart of said patient during ventricular fibrillation; a power supply; a signal analyzer operatively associated with said detector and configured for determining the likelihood of pulseless electrical activity in said patient after delivery of a defibrillation treatment waveform to said patient; and a controller operatively associated with said power supply and said signal analyzer, said controller configured for delivering a defibrillation sequence, said defibrillation sequence optionally comprising a first treatment waveform, said first treatment waveform insufficient to defibrillate said heart, and then delivering a second treatment waveform that defibrillates said heart and restores organized electrical activity in said heart. The first treatment waveform is delivered when a high likelihood of pulseless electrical activity after defibrillation is determined, and said first treatment waveform is not delivered when a low likelihood of pulseless electrical activity after defibrillation is determined.
The foregoing and other objects and aspects of the present invention are explained in greater detail in the drawings herein and the specification below.